The invention relates to a pliable bobbin for the formation of spools of yarn to be dyed, having at least one section which is plastically pliable in the axial direction under the action of a compressive axial load on the bobbin and in which each pliable section is delimited by two rings which are mutually connected by means of flexible elements.
More specifically, the invention relates to a bobbin for dyeing spools having an openwork wall on which is wound the yarn for forming the spool, formed by a plurality of rings which are mutually connected by a series of inclined bridges, deformable under the action of the axial compression of the bobbin. In a bobbin of this type, which is known for example from EP--A--O, 348, 721, there are also provided--between contiguous rings, or between two parts of a bobbin--elements having a predetermined and limited resistance to the axial load. A bobbin of this type behaves as a rigid bobbin until the axial load applied, thereto exceeds a predetermined value, at which point the section, or at least one section, or a plurality of sections of the bobbin yield as a result of the breaking of the connections, causing a reduction in the axial dimension of said bobbin. In the act of yielding, however, appendages form which may become deformed in an irregular manner and form obstacles either to the manipulations of the bobbin or to the taking-up of the yarn. Moreover, the deformation of the appendages may cause excessive compression of the bobbin and of the spool.
In another known bobbin, only inclined bridges are provided between the contiguous rings forming the bobbin, some of which bridges are provided with enlargements or appendages which limit the axial deformation of the bobbin. When the bobbin is compressed, the appendages produced on said bridges come to press against the contiguous rings of the bobbin, in a manner such that a sufficient passage for dyeing still remains. However, partly because of the elevated temperatures of the dyeing bath in which the compression of the bobbin takes place, the appendages are subject to deformation. The deformation of the appendages causes an excessive axial compression, with a reduction of the dyeing passage, and even in some cases the pinching of the thread, with consequent dyeing defects and disadvantages similar to those of the bobbins of the type described in EP-A-0,348,721.